The invention relates firstly to a piping system for chemical liquids, in particular oil products, such as fuels, at least comprising a double-walled plastic conveyor pipe with an inlet and an outlet, the double-walled pipe comprising, in the double wall, one or more intermediate spaces extending along the length of the pipe, and gas-conveying means which are connected to the intermediate spaces for guiding gas through the intermediate spaces.
Piping systems of this nature are generally known in the prior art. One example of such system is described in EP-A-0 753 729. This European patent application describes a device for detecting leaks in double-walled pipelines for petrochemical liquids or gases. The double-walled pipelines comprise an inner pipe which conveys the petrochemical liquid or the gas and an outer pipe. Intermediate spaces are present between the inner pipe and the outer pipe. Gas is held at a specified excess pressure in these intermediate spaces. The pressure is continuously monitored in order to detect any leaks. Furthermore, at regular intervals the gas in the outer pipe is circulated past sensors which are able to establish the presence of any evaporated petrochemical liquid or of gas.
In practice, this has proven to be a reliable way of detecting leaks.
However, a further problem is encountered in the technical field of the double-walled plastic conveyor pipes described in the introduction. This problem is that pipes of this nature have proven not to provide a complete seal for many chemical liquids and, in particular various hydrocarbons from fuel. In fact, it has been found that a certain amount of hydrocarbons penetrates through the walls of the pipe to the environment as a result of what is known as xe2x80x9cpermeationxe2x80x9d. In a large number of countries, the authorities have stipulated that leakage (permeation) of this nature must be minimized. It is even the case in some countries that no permeation of substances through the walls of the pipe into the soil is permitted at all. However, hitherto no satisfactory solution has been found for controlling the permeation effect.
In EP-A-0 753 729, the intermediate space between the inner and outer pipes is under continuous pressure. This retards the evaporation of any substances which permeate out of the inner pipe.
Moreover, the gas mixture in the intermediate space is stationary for most of the time. As a result, substances which permeate through the inner pipe may build up in the intermediate space. This offers the substances the option of also permeating through the outer pipe to the environment.
However, above all there is a risk that the gas mixture including any permeated substances will be pressed through the outer pipe, for example in the event of a leak in the outer pipe. This runs the risk of the soil and the further environment being seriously contaminated with chemical substances.
The object of the present invention is to provide a solution to the above problem and, to this end, the invention is characterized in that the gas-conveying means comprise a gas-suction device which is connected to the intermediate spaces in such a manner that, in operation, gas can be sucked through the intermediate spaces.
As a result of gas being discharged, preferably continuously, from the intermediate spaces with the aid of a suction device, any quantity of chemical liquids, such as hydrocarbons, both in gas form and in liquid form which has penetrated through the inner pipe into the intermediate spaces will be discharged. The sucking action of the suction device generates a subatmospheric pressure. Consequently, the chemical substances evaporate more quickly. Moreover, the possibility of gas or liquid being pressed out of the outer pipe is avoided altogether. Consequently, leakage into the soil is completely impossible, and as a result a completely permeation-tight system is obtained.
Chemical liquids mean in particular petroleum products, such as fuels and the like. In the remainder of the application, however, the text will only refer to fuel, although the present invention is, of course, in no way limited to this particular application and is able to counteract the effect of permeation and leakage in any form. The chemical liquids may be all kinds of environmentally hazardous liquids which must not reach the environment.
The gas-suction device may be designed in numerous ways, but preferably comprises a vacuum pump with an explosion-proof electric motor.
All kinds of gases can be sucked through the intermediate spaces in order to remove any fuel which has penetrated into these spaces through permeation or leakage, but preference is given to air. Advantageously, for this purpose the intermediate spaces furthermore are in optionally direct communication with the environment, so that atmospheric air can be sucked through the intermediate spaces.
More advantageously, the intermediate spaces are connected to the gas-suction device at one end and are in optionally direct communication with the environment, for example via a non-return valve, at the other end. This embodiment will be explained in more detail below in the description of the figures.
Piping systems according to the invention can be used for numerous applications. Consideration may be given to supply pipes for storage tanks, discharge pipes from storage tanks to delivery points or installations, conveyor pipes leading to a floating store, pipes for use in the chemical and petrochemical industry and refineries, petrol stations, etc. With regard to its application, the piping system according to the invention is not subject to any particular limitations.
The invention furthermore provides a petrol station at least comprising one or more fuel storage tanks, one or more fuel delivery points, fuel-conveying means and a piping system for connecting the fuel storage tanks to the fuel delivery points, which petrol station is characterized in that it comprises a piping system according to the invention.
The piping system according to the invention is particularly suitable for use in a petrol station, since in such stations very large quantities of fuel are guided through underground piping systems from fuel storage tanks to delivery points. In these stations, there is a constant risk of permeation.
A petrol station is intended to mean a fuel station where, in addition to petrol, it is also possible to fill up with other fuels, such as diesel, LPG, etc.
Petrol stations usually use suction to suck out full vapours formed while filing up, which is usually located in the vicinity of the delivery opening of the filling nozzle. The gas-suction device may be a similar system.
The gas-conveying means according to the invention may also be coupled to a leak detection system. In this case, consideration may be given to certain sensors in the gas outlet from the intermediate spaces in the pipes, in particular the air outlet, so that any fuel leakage can be detected. If appropriate, this leak detection system may be combined with the suction device.
It is also possible to monitor the pressure difference or the flow rate difference between the inlet and the outlet of the intermediate spaces. The difference in flow rate may be monitored at the entry to and exit from the intermediate spaces of each pipeline, but also of the entire system. The current consumption of the suction device may also be monitored. These options may be combined with a liquid separator.
Finally, the invention provides a method for operating a petrol station according to the invention, in which a gas is sucked through the intermediate spaces at least periodically.
Preferably, the amount of gas per pipe is 1-100 L per h, more preferably 2-50 L per h, and most preferably approximately 20 L per h.
The suction may take place either continuously or intermittently. In particular, the gas is sucked through the intermediate spaces intermittently at a frequency which depends on the number of underground pipeline from the tank(s) to the delivery points and on the capacity of the pump. By way of example, the frequency is 1 minute per 10 minutes of suction.
In particular, the gas comprises atmospheric air.